1. Field of the Invention
The present invention relates generally to a fluid-filled type vibration damping device that utilizes vibration damping effect on the basis of the flow action of the fluid filling the interior. More particularly, the present invention pertains to a fluid-filled type active vibration damping device capable of exhibiting active vibration damping effect by exerting the oscillation force generated by an electromagnetic actuator on an intermediate chamber.
2. Description of the Related Art
Conventionally, there is known a vibration damping device including: a first mounting member attached to one component of the vibration transmission system; a second mounting member attached to the other component of the vibration transmission system; and a main rubber elastic body elastically connecting the first and second mounting members. Such a vibration damping device is applied to an automotive engine mount or the like, for example. There is also known a fluid-filled type vibration damping device further including: a pressure-receiving chamber whose wall is partially defined by the main rubber elastic body; an equilibrium chamber whose wall is partially defined by a flexible film; and an orifice passage interconnecting the pressure-receiving chamber and the equilibrium chamber in order to attain vibration damping effect utilizing flow action of the fluid sealed therein. Additionally, there has been proposed a fluid-filled type active vibration damping device further incorporating an intermediate chamber whose wall is partially defined by an oscillation member oscillated by an electromagnetic actuator, and is capable of exhibiting active vibration damping effect by exerting pressure fluctuations within the intermediate chamber on the pressure-receiving chamber through a pressure transmission passage. Such a device is disclosed in Japanese Unexamined Patent Publication No. JP-A-2009-162281.
It has been attempted on the fluid-filled type active vibration damping device as to providing another orifice passage in addition to the orifice passage connecting the pressure-receiving chamber and the equilibrium chamber, with the aim of achieving vibration damping effect against vibrations in multiple frequency ranges. For example, the aforementioned Japanese Unexamined Patent Publication No. JP-A-2009-162281 discloses a structure in which a second orifice passage is provided for connecting the intermediate chamber and the equilibrium chamber, in addition to the orifice passage connecting the pressure-receiving chamber and the equilibrium chamber.
However, further research conducted by the inventors has shown that, in some instances, the second orifice passage connected to the intermediate chamber may appreciably deteriorate the active vibration damping effect based on pressure control of the intermediate chamber by the oscillation member.
This problem is likely to occur with map control rather than feedback control when employed as control means of the electromagnetic actuator. Accordingly, the inventors supposed that this problem was caused by such an instance that the pressure control was not able to follow the sharp change in spring characteristics due to resonance action of the second orifice passage. Therefore, the inventors addressed removal of the second orifice passage connecting the intermediate chamber and the equilibrium chamber.
However, it has led to the discovery that mere removal of the second orifice passage will not sufficiently improve the vibration damping characteristics, and poses an inherent problem of difficulty in obtaining the sufficient active vibration damping effect based on pressure control of the intermediate chamber by the oscillation member.